In recent years, the piping to be arranged below the automobile, such as the oil-pressure piping for the power steering, the fuel piping such as the main piping, the return piping or the evaporation piping of the fuel and other piping is mostly exemplified by the resin-coated metal tube which has a resin-coated layer formed at least in a thin film shape or, if necessary, in a thick film shape so as to give the chipping-resistance and the splashing resistance.
Moreover, this coated metal tube is prepared by forming a chromate film, if necessary, over the plated layer plated with zinc or zinc/nickel on the outer circumference of the metal tube by the electric, chemical or melting method, by coating thereover an epoxy primer and polyvinyl fluoride (PVF) of a thickness of about 20 microns, and further by covering a heat-shrinkable tube all over its length to form a polymer-coated layer. Another known coated metal tube is prepared by extrusion-molding a resin such as a polyamide resin (PA) such as PA11 or PA12 having a thickness of about 200 to 300 microns or a polypropylene resin (PP) having a thickness of about 1 mm over the zinc- or zinc/aluminum-plated layer applied to the outer circumference of the metal tube.
The outer resin layer of the coated metal tube or polymer coated metal tube has to be removed in advance, in case the tube is to be subjected to a terminal working such as the grooving, spooling, bulging or flaring treatment or to be formed to have the grip portion by the clamp member. This resin layer peeling method can be exemplified by a cutting method. However, this cutting method cannot remove the resin layer homogeneously due to uneven precision of uneven target metal tube, such as the variation in the circularity, the straightness, the external diameter, the thickness of each layer and so on. In some case, the cutting edge may scrape or damage the underlying plated layer or the resin layer to be left as the inner layer. Another difficulty is to take troubles and time, because the underlying plated layer and the resin layer to be left as the inner layer have to be peeled homogeneously without any damage when peeling the resin layer peeling.
Therefore, we have previously proposed a method for peeling a resin layer from a resin-coated metal tube, which can peel off the resin layer remarkably simply and reliably without damaging the substrate and which can peel off only the outer layer even in the case of the polymer-coated resin layer is provided, if the outer layer is made of a softer resin than that of the inner layer (as referred to JP-A-11-82820).
This method has it as one of main features that, when a resin layer is to be peeled off from a resin-coated metal tube which is coated with the resin layer after prime-coated on its outer circumference, the resin layer is pushed by a peeling roll which pushes the resin layer radially inward from the outside and the metal tube and the pushing means are moved circumferentially relative to each other. FIG. 13 is a schematic diagram showing one example of the method. A resin layer (of an epoxy resin, PVF, polypropylene, polyethylene or a polyamide resin) 1-2 is peeled off by turning and pushing a plurality of peeling rolls 3, as arranged concentrically of a metal tube 1-1 made of a steel pipe having a diameter of about 20 mm or less, onto the resin layer 1-2 of a resin-coated metal tube 1 having the metal tube 1-1 coated on its outer circumference with the resin layer 1-2.
According to this method, there can be attained the effects to peel off the resin layer remarkably simply without damaging the substrate and to peel off the outer layer exclusively even in case the polymer-coated resin layer is formed, if the outer layer is made of a softer resin than that of the inner layer.
If the resin layer 1-2 of the resin-coated metal tube is pushed radially inward from the outside by the peeling roll 3, the resin layer 1-2 is extended to have its inner circumference extended by the pushing and turning peeling roll 3, although it is not clear why the resin layer is peeled off from the outer circumference of the metal tube 1-1. It seems that a separation is caused by the turns of the roll 2 in the interface with the extended inner circumference of the resin layer 1-2 so that only the resin layer 1-2 is peeled off.
Of the resin-coated metal tube, however, in case of a resin-coated metal tube, which is coated with nylon having an especially high rust preventing performance, when the nylon coating is subjected to the aforementioned method shown in FIG. 13 to be removed, there arises a problem that a bur 1-2′ of nylon, as called the “Hige” or “Dama”, occurs at the removed boundary, as shown in FIG. 14. This burr may cause problems such as the occurrence of contamination or the reduction in the sealing property so that it has to be removed by means of a cutter or the like. This undesirably increases the number of steps.
As countermeasures against those problems, we have also proposed a method for removing a resin layer (as referred to JA-2002-143398) without forming the burr called the “Hige” or “Dama” at the boundary portion by the aforementioned method using the peeling roll, even for the resin-coated metal tube which has been coated with nylon to have a high rust preventing ability.
In this method, as shown in FIG. 15 and FIG. 16, a resin layer 11-2 is pushed by a peeling roll 12 pushing radially inward from the outside, and a metal tube 11-1 and the peeling roll 12 are moved circumferentially relative to each other thereby to peel and remove the resin layer 11-2. This method is characterized in that a rolled portion 15 (FIG. 16) is formed to have a step and/or dent smaller than the thickness of the resin layer, by pushing means of a roll 12-1 in the resin layer 11-2 at the portion corresponding to the boundary portion of the pushing portion of the peeling roll 12.
According to this method, the resin layer can be removed remarkably simply and reliably without damaging the substrate and without forming the burr called the “Hige (sharp burr)” and “Dama (bead burr)” at the end portion.
In JP-C-3346580, on the other hand, there is disclosed a method for removing a resin layer from a resin-coated metal tube by using a laser beam. This method gasifies and removes a resin-coated layer by defocusing the laser beam in the tube axis direction in a circular section shape or generally in an elliptical shape. This method for removing the resin layer with the laser, as disclosed in JP-C-3346580, can remove the resin layer without leaving unremoved portion or forming the burr. Moreover, the method can remove the resin layer without damaging the substrate of the resin-coated metal tube, the surface-treated layer or the plated layer of the metal tube and so on, and can remove one or more layers of a multi-layered resin film.